The present disclosure relates to the subject matter contained in Japanese Patent Application No.2002-021336 filed on Jan. 30, 2002 and Japanese Patent Application No.2002-021359 filed on Jan. 30, 2002, which are incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to position locating for locating the position of a mobile unit such as a moving vehicle or a person and in particular to a position information transmission apparatus installed in a mobile unit for transmitting position information provided by detecting the position of the apparatus to the outside, a position information transmission method, and a program. This invention also relates to a position locating system, a server, a position locating method, and a program for locating the position of a moving vehicle, a person, etc.
2. Description of the Related Art
In recent years, a position locating system using position detection means such as GPS (Global Positioning System) and base station information of PHS and a mobile telephone to locate the position of a moving vehicle, a person, etc., has been used. For example, as a system for a third party at another location to check the position of an arbitrary object, position locating service or the like is available wherein a mobile terminal having a GPS function is installed in a vehicle or a person and a management service company of the mobile terminal acquires position information in response to demand for providing position information from a client (third party) and transmits the position information to the mobile telephone or PC terminal of the client. The client can check the current position of the objective person or vehicle on a map displayed on a display of the mobile telephone, the PC terminal, etc., and a mark shown in the map.
Since the position locating system detects the position by radio wave and also uses radio wave when obtained position information is transmitted to another location, it becomes impossible to conduct communications in a location at which radio wave does not arrive (for example, tunnel, underground parking lot, dead space area of radio telephone network, etc.,) and it is made impossible to acquire the position information; this is a problem of the position locating system. Specifically in the example of the position locating service, when the client sends the demand for providing position information, if the vehicle already enters a communication-impossible location as mentioned above, a situation in which the position of the object cannot be located at all occurs.
As described above, the position locating system in the related art transmits the position information by radio wave and locates the current position based only on the position information. Thus, if the object enters a communication-impossible location and the position information from the object cannot be acquired, it is made entirely impossible to locate the position.
However, when the object needs always to be tracked as the purpose of locating the position is to find out a stolen vehicle or to care for a person, if the object enters a communication-impossible location and it is made impossible to locate the position of the object, it is fatal.
Also, in such a system, the position information is transmitted at a predetermined frequency from the client apparatus to the server. Preferably, the transmission frequency is high to improve the position locating accuracy, but the transmission cost is increased. Thus in fact, the position information is transmitted every expiration of a predetermined time or each time the mobile unit moves a predetermined distance.
However, if the position information transmission frequency is determined simply by the expiration of the time or the traveled distance, the number of pieces of position information that can be acquired varies depending on the move circumstances of the mobile unit or an excessive amount of position information is transmitted; this is a problem.
For example, with a client apparatus set so as to transmit position information every minute, a mobile unit running at 30 km/h and a mobile unit running at 60 km/h differ twice in the interval between the positions located every transmission.
FIG. 13 shows the above-described circumstances and is a schematic drawing to show the search result displayed on a display of the operator who makes a position search. On the map, a move history of the mobile unit is displayed. The position progression of the mobile unit running at 30 km/h is displayed at small intervals (FIG. 13(a)), but the position progression of the mobile unit running at 60 km/h is displayed at larger intervals (FIG. 13(b)) and the number of pieces of position information that can be acquired at a given distance is lessened. The higher the run speed, the more remarkable the circumstances. In contrast, if the speed is low as in a city, etc., display is produced as in FIG. 13(c). That is, an excessive amount of position information is transmitted even at a short move distance, resulting in waste of the communication cost.
To solve the problem as in FIG. 13(c), setting of transmitting position information every predetermined traveled distance is considered to be effective, but also involves a problem. For example, with a client apparatus set so as to transmit position information every km of traveled distance, for example, if the mobile unit almost stops because of a traffic jam, position information is not transmitted over a long time and thus the server cannot acquire position information; if the mobile unit runs at extremely high speed on a freeway, etc., position information is frequently transmitted, thus resulting in waste of the communication cost.
If only the expiration of a predetermined time or only a predetermined move distance is used as the reference of the position information transmission frequency as described above, the number of pieces of position information that can be acquired varies depending on the move speed of the mobile unit and the communication cost is also wasted.
In recent years, a system has been known for locating the position of a mobile unit based on the already acquired position information in a server if position information from the mobile unit cannot be acquired because the radio wave condition is poor. Since such a system estimates the current position of the mobile unit from the history of a plurality of pieces of position information already acquired before the position information from the mobile unit stops dead, if the number of pieces of position information that can be acquired varies depending on the move circumstances of the mobile unit, precise position estimation cannot be conducted and the estimation accuracy becomes poor; this is a problem.
It is therefore an object of the invention to provide a position locating system, a server, a position locating method, and a program for making it possible to locate the position of an object by estimating the position of the object even if position information from the object whose position is to be located cannot be acquired.
It is also another object of the invention to provide a position information transmission apparatus for changing the transmission frequency of position information of the apparatus in response to the move circumstances of the mobile unit installing the position information transmission apparatus and enabling a server to always acquire constant position information independently of the move circumstances of the mobile unit, a position information transmission method, and a program.
According to the invention, there is provided a position locating system including a client apparatus (client apparatus 1) for detecting current position of the client apparatus and transmitting obtained position information at a predetermined frequency, an information terminal (information terminal 3) for transmitting an instruction for searching for the current position of the client apparatus, and a server (server 2) for receiving the current position search instruction from the information terminal and transmitting map image data containing the current position of the client apparatus to the information terminal based on the position information transmitted from the client apparatus. The server includes a position estimation section (position estimation section 25) for estimating the current position of the client apparatus based on the already acquired position information when the server cannot acquire the position information from the client apparatus and the server requests the client apparatus to transmit position information in response to the search instruction from the information terminal.
According to the invention, there is provided a server (server 2) including a transmission-reception section (transmission-reception section 21) for receiving position information from a client apparatus at a predetermined frequency, receiving a position search instruction from an information terminal, and transmitting map image data containing current position of the client apparatus to the information terminal, a position locating processing section (system control section 20) for generating the map image data containing the current position of the client apparatus located based on the position information transmitted from the client apparatus, and a position estimation section (position estimation section 25) for generating the map image data containing the current position of the client apparatus estimated based on the already acquired position information when the position information from the client apparatus cannot be acquired and the client apparatus is requested to transmit position information in response to the search instruction from the information terminal.
According to the invention, there is provided a position locating method comprising a position information transmission step (S106) wherein a client apparatus detects the current position of the client apparatus and transmits obtained position information at a predetermined frequency; a search instruction transmission step (S301) wherein an information terminal transmits an instruction for searching for the current position of the client apparatus; a position information estimation step (S405) wherein a server receives the current position search instruction from the information terminal, requests the client apparatus to transmit position information, locates the current position of the client apparatus based on the position information transmitted from the client apparatus, and estimates the current position of the client apparatus based on the already acquired position information if the server cannot acquire position information from the client apparatus when the server requests the client apparatus to transmit position information in response to the current position search instruction; and a position information transmission step (S406) of transmitting map image data containing the current position of the client apparatus located or estimated in the server to the information terminal.
According to the invention, there is provided a position locating method executed by a server comprising a position information estimation step (S401 to S405) of receiving a current position search instruction from an information terminal, requesting a client apparatus to transmit position information, locating the current position of the client apparatus based on the position information transmitted from the client apparatus, and estimating the current position of the client apparatus based on the already acquired position information if position information from the client apparatus cannot be acquired when the client apparatus is requested to transmit position information in response to the current position search instruction; and a position information transmission step (S406) of transmitting map image data containing the located or estimated current position of the client apparatus to the information terminal.
According to the invention, there is provided a program executed by a server for causing a computer to function as a transmission-reception section for receiving position information from a client apparatus at a predetermined frequency and receiving a position search instruction from an information terminal and transmitting map image data containing the current position of the client apparatus to the information terminal, a position locating processing section for generating the map image data containing the current position of the client apparatus located based on the position information transmitted from the client apparatus, and a position estimation section for generating the map image data containing the current position of the client apparatus estimated based on the already acquired position information when the position information from the client apparatus cannot be acquired and the client apparatus is requested to transmit position information in response to the search instruction from the information terminal.
According to the invention, even if the position information cannot be acquired from the client apparatus whose position is to be located, the server estimates the current position of the client apparatus based on the already acquired position information, so that it is made possible to locate the position of the object.
According to the invention, there is provided a position information transmission apparatus being installed in a mobile unit for detecting the position of the apparatus and transmitting acquired position information to a server for locating the position of the apparatus, the position information transmission apparatus a position information transmission frequency setting section (position information transmission frequency setting section 20) for setting transmission frequency of the position information in response to move speed of the mobile unit.
According to the invention, there is provided a position information transmission method for detecting the position of a mobile unit and transmitting acquired position information to a server for locating the position of the mobile unit, the position information transmission method comprising a speed determination step (S102) of determining move speed of the mobile unit; and a transmission frequency setting step (S103, S105, S107, S109) of setting transmission frequency of the position information in response to the move speed of the mobile unit.
According to the invention, there is provided a program for detecting the position of a mobile unit and transmitting acquired position information to a server for locating the position of the mobile unit, said program for causing a computer to function as a section for determining move speed of the mobile unit, and section for setting transmission frequency of the position information in response to the move speed of the mobile unit.
According to the above-described configuration, the position information is transmitted based on the transmission frequency set in response to the move speed of the mobile unit and thus can be transmitted at the optimum frequency responsive to the move circumstances, so that the server can always acquire constant position information independently of the move circumstances.